Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan with butter or line it with parchment paper.

In a large mixing bowl, whisk together 2 cups of flour, 1 teaspoon of baking powder, 1/2 teaspoon of baking soda, and 2 teaspoons of cinnamon until well blended.

In another bowl, whisk together 2 eggs with 1 cup of sugar until smooth and frothy, then mix in 1/2 cup melted butter and 1 cup sour cream until creamy.

Gradually incorporate the dry ingredients into the wet ingredients, stirring gently until just combined.

Fold in 3 cups of diced apples using a spatula, ensuring even distribution.

Pour the batter into the prepared baking pan and smooth the top.

Bake in the preheated oven for 45-55 minutes, until golden brown and a toothpick comes out clean.

Let the cake cool in the pan for 15-20 minutes, then transfer to a wire rack to cool completely.